The invention relates to a device for cooling, drying, and granulating molten strands issuing from nozzles and made, e.g., from thermoplastics, with an outlet channel, the upper end of which is located below the nozzles, a device, generating a current of cooling liquid over the outlet channel, a granulator arranged downstream of the outlet channel and with a dehydrating section that is arranged upstream of the granulator and in which the strands rest on a support provided with orifices for the unrestricted passage of the cooling liquid.
Such a device is known from the DE-PS 33 36 032. In this device the dehydrating section comprises zones of which the first zone in the flow direction leads to a water outlet and the second zone is pressurized with an air current, by means of which water clinging to the strands is largely sucked off. These two zones of the dehydrating section are arranged practically directly upstream of the granulator.
The invention is based on the problem of further improving the known device, described above, with respect to its drying efficiency and simultaneously giving the device especially good self-threading properties.
The invention accomplishes this in that the outlet channel in the region following the dehydrating section is provided with inlet nozzles that inject a current of fluid and that are so close together and arranged over such a length in its bottom that the strands are guided with respect to the bottom virtually without friction along the outlet channel into the granulator, arranged at its lower end, with a degree of dehydration that enables immediate further processing.
The result of inserting the region of the inlet nozzles guiding the current of fluid between the dehydrating section and the granulator is the combination of two effects. On the one hand, the strands are dried to the extent that they are processed by the granulator with a degree of dehydration that enables immediate further processing, i.e. the granules that are produced do not require any subsequent drying process. The current of fluid provides that the strands are subsequently guided virtually without friction over the bottom, a feature that is especially significant due to the lack of water, which, when present, acts to some extent as a lubricant. The virtually frictionless guiding of the strands in the region of the inlet nozzles provides that the strands, pushed forward by gravity or the current of cooling liquid, automatically obtain a tendency to self-thread, which is otherwise decreased in the area upstream of the granulator when cooling liquid is lacking.
The tendency for self-threading can be further intensified by sloping the inlet nozzles in the direction of motion of the strands.
Preferably a current of gas, in particular a current of air, is used for the current of fluid. It is also possible to use an inert gas, in particular nitrogen, which is frequently produced in chemical operations as a side product.
To be able to process especially moisture-sensitive substances, a powdery drying agent is added in an advantageous manner to the current of gas. Usually such a drying agent also has the effect of preventing the strands from sticking together. If such a drying agent is undesired for the further processing of the granules since said drying agent adheres to the manufactured granules, the outlet channel between the granulator and the region of the inlet nozzles guiding the current of fluid can be provided with perforations leading to a suction chute. Then a current of air sucked in through the suction chute and the perforations removes the powdery drying agent from the strands so that the strands are conveyed virtually without any drying agent into the granulator.
To increase the feed effect of the sloped inlet nozzles, feed nozzles for blowing a current of fluid against the strands in the direction of movement of the strands can be provided in an advantageous manner in the region of the inlet nozzles above the outlet channel. Preferably the same medium is used for this current of fluid as for the current of fluid directed through the inlet nozzles. These additional feed nozzles also increase the tendency towards self-threading. This is especially advantageous if the inlet nozzles provided in the bottom of the outlet channel pass vertically through the bottom.
To adapt the device to different drying and cooling needs, the region of the inlet nozzles guiding the current of fluid and/or the region upstream of the dehydrating section is/are lengthwise adjustable. To this end, a telescopic construction of the regions in question is especially suitable. In this manner it is possible to combine an especially long section guiding the current of cooling liquid with a shortened length of the region with the inlet nozzles for the current of fluid.
To obtain special drying, cooling or heating effects, the current(s) of fluid can be suitably moderated. Thus, for example, it is desirable to heat fiber-reinforced plastic strands by means of the current of fluid in order to thus remove the load from the granulator. Vice versa it is advantageous for granulating flexible strands to cool them prior to granulating, since in this case better granules are obtained.